Too close to call. If sex is with one person (monogamous), the dates shouldn't matter. If not monogamous, a woman should keep different guys at least two (2) weeks apart, in order to figure out who's the daddy. Otherwise, it is "too close to call". An old-fashioned way has worked for thousands of years (the husband of the woman is the father). The new way works too (doing a DNA test on the baby and one of the men).